Is this normal?

I have 8 three week old chickens that I just put out with my older chickens. (four are adult hens and the other six are between 3 and 4 month old buff cochin chickens). My older hens are fine and actually somewhat protective of the babies, but one of my cochins is bullying them. Is this normal? Will she actually hurt them? Do I need to be concerned?

Yes..your other chickens can be quite ruff to the others. They may even want to hurt them. I wouldn't put them together yet. Give it a few more weeks at least, and make the introduction slowly. You shouldn't just stick them together and hope they all get along. Chickens don't work that way. They need to establish a pecking order and your 3 weekers are to young in my opinion. Give it some more time. They will be bigger so enough. There's lots of introduction topics in BYC. Use the search at the top. That should help you also. Good Luck.

when introducing new birds to a flock there should be a period of time where there is no direct contact between them, like a full chicknwire enclosure for the smallers inside the larger chicken's home.

Chicks dont fully feather till 5-6 weeks and cant make it with the olders outside in extreem weather and should be coddled till then. they are not even close to big enough to attempt to find their place in the pecking order, which will cause lots of disturbance now and later when they finally get big enough to do so.

also could your one mean chick (at 3-4 months) be a cockerel? check out if this bird is top bird, if it is and is overly agressive you may want to think of culling it. some hig agressive to other birds birds become agressive to people as well. And that is not Fun! I had a wing clipped rooster that would jump a 6 foot fence just to attack me, even when I was bringing food or treats.

They have been in a wire enclosed brooder inside of the chicken pen with the others for a couple of weeks now. I think they're actually closer to four and a half or five weeks old (someone in my house told me three, but we've raised them from the day they were born). They have had indirect contact with them for a while now. I'm keeping an eye on them and if the bullying doesn't stop today, the older chicken is getting pinned up by itself for a while. It's the only one of the bunch that's causing any problems. The other chickens have accepted them just fine and the oldest ones even act like they're trying to protect them.

Oh and about the feathers, they are fully feathered. We wouldn't have put the out if they weren't. They had all their feathers before we ever put them in the outside brooder.